Pesticide Resistance, Population Dynamics, and Invasive Species Management

This report describes a dynamic bioeconomic simulation model that represents the biological, economic, and regulatory features of a specific invasion management problem: the late 1990s invasion of California strawberries by the greenhouse whitefly, Trialeurodes vaporariorum, and the pesticide use restrictions imposed by California regulators to manage pesticide resistance. The model has three components: the population dynamics of the greenhouse whitefly, a population-yield damage function, and grower profit maximization. Use regulations are introduced as constraints on the grower’s decision. The cost of the regulations during a single season resulted in the restriction to 2 or fewer applications of pyriproxyfen which always reduced profits. Applying imidaclopid at planting always increased profits. The regulation, which restricts use of imidacloprid at planting only, does not offset the cost of the restriction to 2 or fewer applications of pyriproxyfen per season. Instead, a third application of pyriproxyfen and imidacloprid are complements, so the cost of the 2-application limit per grower is larger when imidacloprid is applied at planting. The requirement regarding the timing of the first application of pyriproxyfen reduced profits. Comparing the regulations’ benefit in slowed resistance to the reduction in profits over a 6-year period shows that there are some conditions under which use regulations provide a net benefit. Regulation, however, does not substitute for coordination among growers when seeking to control the greenhouse whitefly. Greater profits are possible through coordination, even under regulation.